Here are two paragraphs that tell the story very well, and in a very moving way:

Rather than denounce the Bible as fraudulent along with its white adherents, the slaves recognized that learning to read the Bible and to possess its contents for themselves was real spiritual power, whose potency was made all the more alluring by efforts to prohibit its access. So, slaves vowed to learn to read before they died so that they could read the Bible. They took advantage of every clandestine opportunity to secure lessons from favorable masters or their children, often risking legally sanctioned retribution, severe beatings and death.

By the end of slavery’s reign in America, African American doctrines of revelation were beginning to widen and make room for sources of revelation other then the Scriptures, including God continuing to reveal himself through supernatural means and interventions. This expansion of the doctrine of revelation would weaken the centrality of the Scriptures in the practice and thought of African American Christianity.